Time travel into the future is already possible

Time travel happens all the time: we're usually travelling smoothly into the future at the rate of one second per second. We can also slow down the flow of time with high speed and high gravity, but as Dr Karl Kruszelnicki explains, going backwards is a bit more complicated.

There are two types of time travel: into the future, and into the past. Past time travel might be impossible, but on the other hand, we already travel into the future all the time.

Is time travel into the past theoretically possible? Again, we haven't proved that it is, but on the other hand, we haven't proved that we can't.

On average, we are all travelling smoothly in the future at the rate of one second per second.

But Einstein's theories of special and general relativity have given us two ways to slow this flow of time down: speed and gravity.

Both high speed and high gravity will slow down the flow of time.

One of the earliest experiments on this was carried out in October 1971. It took over half-a-century for everything to come together, after Einstein's Theory of Special Relativity in 1905, and his Theory of General Relativity in 1915.

It was probably one of the cheapest tests of relativity ever carried out. By the early 1970s, atomic clocks were now precise enough to get sufficiently accurate measurements, as well as being rugged and portable.

Also around that time, the recently introduced Boeing 747 was being taken up by the commercial airline fleets. As a result, international travel was now both fast enough (so the 'slowing' of time was measurable) and cheap enough (for the penniless scientists to afford it).

Joseph C. Hafele, a physicist, and Richard E. Keating, an astronomer, took four caesium-beam atomic clocks on round-the-world trips. They booked four seats: two for themselves, and two for Mr Clock (two seats, each with two atomic clocks).

The total cost of this test of relativity was US$8,000—with over US$7,600 being spent on eight round-the-world tickets. The six of them—two humans and four atomic clocks—flew around the world twice, first eastward, and then westward.

Their results agreed 'reasonably' with relativity. Their initial results showed that time slowed down with increased speed. Later re-enactments of their initial experiment with more sophisticated atomic clocks gave much better agreement with this theory.

But jet planes are slow compared to light. Once you get close to the speed of light—about 300,000 kilometres, or roughly eight times around the Earth, in one second—time really begins to slow down.

A spaceship travelling at 90 per cent of the speed of light, or 270,000 km/s, has its time slow down by a factor of 2.6.

At the moment, the fastest matter, regularly propelled by human technology, are the hydrogen ions (H+) zipping through the 27 km circumference of the Large Hadron Collider.

The hydrogen ions travel at 99.999,999,1 per cent of the speed of light. Their time slows down by a factor of 27,777,778. One second for one of these protons is about 11 months for us.

Like speed, gravity also slows down time. Imagine two atomic clocks on shelves, the upper one being 33cm above the lower one. The upper one experiences slightly less gravity, because it is just a little further from the centre of the Earth.

By the year 2010, our technology had become precise enough we could measure that the lower clock (in the slightly higher gravitational field) was ticking more slowly.

Of course, if you want to talk powerful gravitational fields, we automatically think of black holes. There is an enormous one at the centre of our galaxy, but there's a much smaller one 3,000 light years away. The movie Interstellar has a planet orbiting very closely to a black hole. In the movie, one hour spent on the planet has the people back on earth ageing seven years.

But what about travelling into the past?

Well, back in the year 2009, the famous physicist, Stephen Hawking, hosted a party for time travellers. In 2010, one year later, he sent out the invitations to his party in 2009. Of course, nobody showed up.

Does this prove that time travellers are too busy for parties? Or that time travel into the past is impossible? Of course not (it's just one experiment, et cetera).

But is time travel into the past theoretically possible? Again, we haven't proved that it is, but on the other hand, we haven't proved that we can't.

By the way, it isn't just you having trouble with getting your head around 'wibbly wobbly timey wimey' stuff. Entering the land of theory can be a bumpy ride and do very strange things to your sense of equilibrium.

David :

14 Sep 2016 10:08:32am

Re Dr Karl's statement "Is time travel into the past theoretically possible? Again, we haven't proved that it is, but on the other hand, we haven't proved that we can't." I believe that the laws of thermodynamics, and in particular entropy, offer a fairly robust argument against the possibility of traveling backwards in time.

Franco :

21 Sep 2016 7:34:49pm

The time traveller's constituent energy and matter is being used elsewhere in the earlier time period - for example in a tree, rocks, a porcupine, and countless other things. His or her successful and sustained insertion into the past would, in effect, require the creation and/or injection of new energy into the universe. A possible violation of the first law, if one considers the universe a closed system.

Ben Lim :

14 Sep 2016 11:23:12am

From reading the description of the atomic clocks experiment on different shelves, the lower clock slowed because it was closer to gravity. My posit is that it is the measurement of time that is slowed and not the concept of time itself, because the atoms are "pulled" by gravity and thus slowing it down compared to the upper shelf clock. Therefore, the measurement of time will be affected by the strength of gravity. We will still age in three scores and ten years, but how we present that three score and ten years will depend on how and where we measure that.

mcalex :

Brett Gerrity :

14 Sep 2016 5:28:31pm

Mankind should never investigate travelling back in time. Life as we know it would be destroyed if anyone could, "dial up a time".Right the wrongs? Who and what would be left? Nothing.Sure,I would love to go back and confront my tormentors. Those who done me grievous harm. Those wrongs perpetrated against me made me who I am today. An empathetic, compassionate person who only does good. How would I have turned out if I was not subjected to extreme adversity? Selfish? Pompous? Greedy?I love who I am today and I can thank my tormentors for that.

time traveller :

16 Sep 2016 2:33:52am

This is a great article! My only suggestion would be to use a nano-ship with radioactive-resistant bacteria in it instead of humans, using Novikoiv's research: http://timetravelteleporter.blogspot.com/2016/09/the-problem-with-time-travel-is-you.html#comment-form